If it's the amp, it is possible one of those new tubes is microphonic. Try the soft tap method to see, and if so take it back to the shop you got it from. Did you get the cab and tubes from the same...

A while ago I put a Gibson X2N pickup (Gibson's hottest pickup) in my Squier Stratocaster in the bridge and it made a world of difference. Pinch harmonics are easy to hit, and it just screams. I got...